erofs: fix wrong kunmap when using LZMA on HIGHMEM platforms

erofs: fix wrong kunmap when using LZMA on HIGHMEM platforms

As the call trace shown, the root cause is kunmap incorrect pages:

 BUG: kernel NULL pointer dereference, address: 00000000
 CPU: 1 PID: 40 Comm: kworker/u5:0 Not tainted 6.2.0-rc5 #4
 Workqueue: erofs_worker z_erofs_decompressqueue_work
 EIP: z_erofs_lzma_decompress+0x34b/0x8ac
  z_erofs_decompress+0x12/0x14
  z_erofs_decompress_queue+0x7e7/0xb1c
  z_erofs_decompressqueue_work+0x32/0x60
  process_one_work+0x24b/0x4d8
  ? process_one_work+0x1a4/0x4d8
  worker_thread+0x14c/0x3fc
  kthread+0xe6/0x10c
  ? rescuer_thread+0x358/0x358
  ? kthread_complete_and_exit+0x18/0x18
  ret_from_fork+0x1c/0x28
 ---[ end trace 0000000000000000 ]---

The bug is trivial and should be fixed now.  It has no impact on
!HIGHMEM platforms.

Fixes: 622ceaddb764 ("erofs: lzma compression support")
Cc: <stable@vger.kernel.org> # 5.16+
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230305134455.88236-1-hsiangkao@linux.alibaba.com